I understand your frustration: in an ideal world, we should be able to easily reward people who contribute to the greater good, and open source developers are certainly in that category.

However, this reward may not always be money: community recognition and extended network, better chances of hiring, or attribution from projects that depend on you should also be considered.

Yeah, it is valid to say that funding needs to be improved. But while ads provide a way, it is a stretching to call it the only or the right way. Maybe open source development is just fine with corporate sponsorship + people doing it in their free time. Maybe developers are repelled by ads so much that it actually hinders contributing to interesting projects. Maybe charity and donations work better we just haven't figured it out yet (see Patreon, which had a surprising success, despite the skepticism around microfunding).